橡胶 硫化 - 拉伸疲劳的测定

[中文适用范围]： 本文件规定了测定硫化橡胶在重复拉伸变形下的抗疲劳性的方法，试件尺寸和循环频率使得温升很小或没有。 在这些条件下，裂纹的扩展最终会导致试件断裂而导致失效。 该方法仅限于重复变形，其中测试件在每个周期的一部分中松弛至零应变。 类似的疲劳过程可能发生在不经过零应变的重复变形下，并且在某些橡胶中，在静态变形下也会发生，但本文件不适用于这些条件。 该方法被认为适用于至少在循环一段时间后具有相当稳定的应力应变特性并且不表现出过度的应力软化或凝固或高粘性行为的橡胶。 从实验和解释的角度来看，不符合这些标准的材料可能会带来相当大的困难。 例如，对于在疲劳测试过程中产生大量变形的橡胶，测试应变将不明确，并且在恒定最大载荷和恒定最大延伸条件下，疲劳寿命可能会显着不同；如何解释这种橡胶的结果或如何与其他橡胶的结果进行比较，尚未通过基础工作确定。 作为一般指导，根据 9.5 和 10.2 确定的凝固超过 10% 的橡胶可能属于此类。 因此，该方法被认为不适用于大多数热塑性弹性体。 类似的考虑也适用于测试期间弹性行为的其他变化。 该疲劳测试与 ISO 4666 各个部分中描述的屈曲测试不同，其中疲劳破坏是在应力和温度的同时作用下发生的。 相对于 De Mattia 挠曲裂纹和切口增长测试（参见 ISO 132）的优点包括： ——测试产生的定量结果不依赖于操作员的解释，并且可以自动记录； ——初始变形被明确定义，并且可以很容易地改变以适应不同的应用。 在尝试将标准测试结果与使用性能联系起来时必须非常小心，因为不同硫化橡胶的相对疲劳强度可能会根据所使用的测试条件和结果比较的基础而变化。 附录 A 给出了测试条件选择和结果解释的指南。 [外文原描述]： ISO 6943:2017 specifies a method for the determination of the resistance of vulcanized rubbers to fatigue under repeated tensile deformations, the test piece size and frequency of cycling being such that there is little or no temperature rise. Under these conditions, failure results from the growth of a crack that ultimately severs the test piece. The method is restricted to repeated deformations in which the test piece is relaxed to zero strain for part of each cycle. Analogous fatigue processes can occur under repeated deformations which do not pass through zero strain and also, in certain rubbers, under static deformation, but this document does not apply to these conditions. The method is believed to be suitable for rubbers that have reasonably stable stress-strain properties, at least after a period of cycling, and that do not show undue stress softening or set, or highly viscous behaviour. Materials that do not meet these criteria might present considerable difficulties from the points of view of both experiment and interpretation. For example, for a rubber that develops a large amount of set during the fatigue test, the test strain will be ill-defined and the fatigue life is likely to differ markedly under constant maximum load and constant maximum extension conditions; how the results for such a rubber should be interpreted or compared with those for other rubbers, has not been established by basic work. As a general guide, a rubber for which the set determined in accordance with 9.5 and 10.2 exceeds 10 % is likely to fall into this category. For this reason, the method is not considered suitable for most thermoplastic elastomers. Similar considerations apply with regard to other changes in elasticity behaviour during testing. This fatigue test is distinct from the flexometer tests described in the various parts of ISO 4666, where fatigue breakdown occurs under the simultaneous action of stress and temperature. Advantages over the De Mattia flex cracking and cut growth test (see ISO 132) include the following: - the test yields quantitative results which do not depend on operator interpretation and which can be recorded automatically; - the initial deformation is clearly defined and can readily be varied to suit different applications. Great caution is necessary in attempting to relate standard test results to service performance since the comparative fatigue resistance of different vulcanizates can vary according to the test conditions used and to the basis by which the results are compared. Guidance on the selection of test conditions and on the interpretation of results is given in Annex A.